Large-Scale Climatic Influences on Baldcypress Tree Growth Across the Southeastern United States

Abstract

Baldcypress trees native to the southeastern United States are extraordinarily sensitive to growing season rainfall amounts and can live for over 1000 years. Baldcypress tree-ring chronologies have been used to develop verifiable reconstructions of March through June precipitation totals representing some 50 to 70% of the instrumentally-recorded rainfall variance. These rainfall reconstructions are dominated by high interannual variability, but also include decade-scale fluctuations representing some 10% of the reconstructed rainfall variance. Decadal variations of similar magnitude are also evident in the instrumental March-June rainfall data, and may in part reflect secular changes in large-scale climatic forcing. To explore this possibility, we performed principal components analysis on the regional network of 11 long baldcypress chronologies from the Southeast, and compared the eigenvector amplitude series derived from the first three significant principal components of tree growth with northern hemisphere 700 mb heights for spring (March-June) from 1948 to 1980. The strongest relationship discovered was between the first principal component of baldcypress growth (PC1) and spring 700 mb height departures over the southcentral United States and northern Mexico. Significant correlations with 700 mb heights over northwestern Canada and over the western North Pacific were also identified. These mid-tropospheric teleconnections with cypress PC1 are similar to the Pacific-North America (PNA) longwave circulation pattern.

The baldcypress PC’s were then compared with indices of the PNA and other large-scale circulation patterns previously linked with seasonal climate anomalies over the southeastern United States. The highest correlations were between cypress PC1 and a PNA and PNA-like index. Much lower, but statistically significant correlations were also observed with indices of the zonal position of the Bermuda High [i.e., based on the second principal component of sea level pressure (SLP PC2) over the western North Atlantic and eastern United States], the North Atlantic Oscillation, and the Southern Oscillation. Cross-spectral analyses indicate that baldcypress PC1 is coherent and out-of-phase with the PNA and PNA-like indices at the 4-year frequency band, and with the Bermuda High index at frequencies ≥4 years. These various circulation influences are not strong enough to account for all sub-decadal to decadal fluctuations in baldcypress growth across the southeastern United States. However, if the baldcypress data are joined with long climate-sensitive tree-ring chronologies from western North America, it may be possible to reconstruct a useful fraction of the longwave circulation variability over the North Pacific-North American sector for the past millennium.